The most recent helium abundance determinations in main sequence B stars are those of Hardrop and Scholtz, Kodaira and Scholtz, Norris, and Leckrone. Their results indicate that it is possible to assign a helium abundance which is characteristic of all B stars. Norris and Leckrone worked with a number of B stars ranging from B0 to B9, and both have assigned a characteristic helium abundance to the B stars. Norris derived a value, A = 0.088 ± 0.012, and Leckrone a value of A = 0.106 ± 0.01, where A is the abundance of helium relative to hydrogen by number.

In this paper we give an account of the corrections that must be made to the formula for the emissivity ηf due to a power-law energy distribution of ultrarelativistic charged particles in a uniform magnetic field B0 in directions well away from the field lines when the effects of upper and lower cut-off values E2 and E1 in the energy distribution are not negligible.

Since 1971, the Llanherne low frequency radio telescope (Ellis 1972) has been used to conduct surveys of the sky at several decametric wavelengths. Prior to 1974, only pen recordings on paper chart for one declination at each of the wavelengths were obtained each night and all the work to produce the final sky maps was to have been done by hand. However in 1974, a general purpose digital minicomputer (a Digital Equipment Corporation PDP 8/E) has considerably increased the research capabilities of the telescope. In the continuum sky surveys profiles at several different declinations are now obtained each night. In addition all the information gathered in an observing session is written onto magnetic tape which is later analysed on the University of Tasmania’s computer (an Elliot-503) thus providing the possibility of removing much of the tedious manual work in preparing the final sky maps. This paper describes the system developed by the author which is used by Cane (1975) to obtain the profiles from which the sky maps are being compiled.

Some while ago (Prentice 1973a) I demonstrated that if the present Sun were to possess a small burnt out central core of mass 2-3% M⊙ its neutrino flux would be a factor 10 or so smaller than that of conventional homogeneously evolved solar models. It was not, however, conclusively shown what conditions might lead to the formation of such a core or indeed whether a burnt out core could be attained after 4.7 × 109 yr. of nuclear evolution. In this connection Demarque et al. (1973) has considered the evolution of an initially inhomogeneous model consisting of a hydrogen free core surrounded by a homogeneous envelope.

An investigation into the influence of rotation on thermal convection has some applicability in the study of the solar convection zone. Of particular interest is the effect of rotation on the total heat transport and the cell size for maximum heat transport at high Rayleigh number, which is estimated to be as high as 1020 for the Sun.

The spectrum of a symbiotic star consists of an M-type absorption spectrum, a B-type shell spectrum and nebula emission lines, the relative contributions of these three components varying with time. The light curves of the symbiotic stars vary with a semi-regular period typically 200-800 days while larger eruptions occur on a timescale of ~ 3.5 years. Some suggestions which have been advanced to explain the combination spectrum, variability and eruptive behaviour of the symbiotic stars are:

1. (a) the symbiotic stars are binaries consisting of a hot and cool component.

2. (b) the symbiotic stars consist of a single hot star surrounded by a large optically thick envelope giving the appearance of a hot continuum with the absorption spectrum of a cool star superimposed on it.

3. (c) the symbiotic stars are single stars surrounded by a shock wave heated chromosphere.

   Although some of the symbiotic stars are undoubtedly binaries (for example, T Coronae Borealis), observatienal evidence suggests that others may be explained by hypothesis (c) above. The calculations described below provide an explanation of the symbiotic stars in conjunction with hypothesis (c).

It is well known that a magnetic field has an inhibiting effect on thermal convection. It is also likely that a magnetic field might have a marked effect on the preferred cell-size and it is therefore of some importance to investigate the effect of such a field on finite amplitude convection. We restrict ourselves to fluids in which the Boussinesq approximation holds. For astrophysical application, especially in a study of the convective layer of the Sun, one should consider the compressible case but unfortunately the full compressible equations are much more difficult to handle numerically. In any case, the integration of the equations for the incompressible case will yield at least an indication of the effect of a magnetic field.

During the past twelve years five series of observations have been made of the polarization of Jupiter’s radio emission at a wavelength of 11 cm. This data shows characteristics which have been stable over a period of years as well as some unexplained variations. The observations were made during one complete orbital period of Jupiter and hence were obtained over the full range of values of DE, the angle between Jupiter’s rotational axis and the plane of the sky. These are summarized in Table 1. The 1967 observations have been reported previously (Komesaroff and McCulloch 1967) and the 1963 data is from Roberts and Komesaroff (1965).

Coudé spectra were obtained for a selection of giant and supergiant stars having spectral types in the range A9 to F2 to determine their atmospheric characteristics. The 12 members of Table 1 were compiled from The Catalogue of Bright Stars. This group of stars includes all known supergiants south of declination −15° and brighter than mv = 5.0 with spectral type between F5 and A5. Delta Canis Majoris (F81a) which has been the subject of many detailed investigations, was also observed to check for possible systematic errors in our equivalent widths. The spectra were obtained using the Coudé spectrograph of the 40 cm reflector at the University of Tasmania Observatory. Linear dispersions of 1.8Å mm−1 (0.12Å resolution) in the range 3600 to 4000Å and 2.4Åmm−1 (0.18Å resolution) in the range 4000 to 5000Å were used for stars brighter than third magnitude; 9Å mm−1 (0.4Å resolution) was used for stars fainter than third magnitude. The classification of 196 Car. was observed to be later (F8III) than the listed value and the spectrum of this star was not analysed further.

Despite the success of the Babcock-Leighton model in explaining some phenomena of the solar cycle, e.g. Hale’s polarity law and Maunder’s butterfly diagram, it has recently encountered a number of observational and theoretical difficulties. The observational difficulties are centred around the different behaviour of bi-polar magnetic regions (BMRs) and uni-polar magnetic regions (UMRs). Babcock explains BMRs as the surface eruptions of toroidal fields wound by the differential rotation and it is clear that in their subsequent evolution and decay they are obviously influenced by this effect. However, UMRs display a sector structure in which the boundaries between regions of opposite polarities appear to be quite unaffected by the differential rotation but closely related to the interplanetary field sectors. Another feature of solar activity unexplained by the Babcock theory is the tendency of sunspots, flares, etc. to reappear at the same latitude during a cycle. Warwick has observed that proton flares show a preference for particular latitudes which may extend over several cycles. Again Bumba et al. have observed that new cycle fields tend to appear in longitude regions where old cycle fields are still visible.

In this paper we obtain an approximate expression for the temperature structure of a stellar atmosphere heated by an external flux of soft X-rays. Allowance is made for reradiation in both the soft X-ray and optical regions. As may be expected our results indicate that the temperature structure will be drastically changed from the grey T-T relation, particularly at low optical depths. The stronger lines should appear in emission with the possibility of a central absorption in certain circumstances. The present results are in general agreement with those of Strittmatter (1974).

DF and DG white dwarfs are the only types which show metal lines (see Greenstein). Presently the only analysis is that of Weidemann who analyzed the star van Maanen 2 and found that the abundances of metals and hydrogen are the order of 10-3 and 10-2 that of solar, respectively. Bues finds H = 1 : 105 and Z = 2 × 10-4 for DB stars.

Dissipation of shock waves has often been proposed as the energy source required to sustain the outward temperature rise in the solar atmosphere. Theoretical models for the heating process have been developed by equating the mechanical energy input to the radiative energy loss at each height, but neither of these processes is well understood, and the lack of data means that the models are necessarily crude.

The region of the solar atmosphere where the brightness temperature is less than 9 x 103 K. defines the photosphere and low chromosphere. In physical scale this covers the range from 300 km. below to 2 x 103 km. above the visible surface.

Prompted by recent moves to ask the International Astronomical Union to redefine the System III rotation period, we have used all available dekametric observations from 1951 to 1975 and new analysis methods in an attempt to improve our estimate of the Jovian dekametric rotation period.

The optical astronomy group at the University of Tasmania is engaged in a search for optical pulsations from pulsars.

It was considered that the PDP-8/F mini-computer, purchased with A.R.G.C. funds to control the 40 inch telescope and on-line experiments, would be extremely useful for this purpose, until completion of the 40 inch telescope. Interfacing the computer to the output of the Cassegrain photo-electric photometer required work at both the hardware and software level.

Some statistics from 368 plates of 111 double stars observed between July 1965 and January 1969 with the Yale-Columbia 26-inch refractor at Mount Stromlo Observatory, are presented. The results of plate measurements, and a description of the work, are to be published elsewhere.

The darkness of sunspots has been attributed by many authors (Biermann 1941; Danielson 1961) to the inhibition of the normal solar convective processes by the presence of strong magnetic fields. Observations of the solar photospheric granulation pattern have also shown that a weak longitudinal field exists outside the activity regions. Although these observations have not revealed any close association between the magnetic field and individual granules, nor the exact reasons for the darker cell boundaries, it must be accepted that, overall, the role of the magnetic field must be such as to influence the cell structure and reduce the normal heat transfer by convection.

In the first four years of operation with the 80 MHz heliograph at Culgoora, 24 events classified as moving type IV were observed. Their observed characteristics can be interpreted in terms of gyro-synchrotron radiation from mildly relativistic electrons. Many of these events have been presented at previous ASA meetings and 12 have been discussed in the literature in detail.

It appears that the relative number of β–Cephei variables among the early B stars is comparable to the fraction of the evolutionary lifetime spent in the secondary contraction and early shell-burning phases (Lesh and Aizenman 1973a) and it may therefore be of some interest to investigate possible instability mechanisms associated with hydrogen shell-burning in stars within the mass range of 10 to 15 M⊙ (Lesh and Aizenman 1973b).